Ammonia in the neutral ring around the galactic centre.

Several metastable NH₃ lines have been detected from the molecular gas which orbits about the center of our galaxy at radii ⪆2 pc. A rotational temperature of ≡95K is estimated for this gas, implying a kinetic temperature of 240±100K. Several spectral features arising from gas along the line of sight to the center have also been detected. Gas at 40 km s^-1 is seen in absorption in the higher lying inversion transitions. From a comparison of the excitation temperatures of the levels with the background continuum temperature, the density of this gas is estimated to be ≡1 - 3x10⁴cm^-3. Also seen are NH₃ absorption features at -135, -51, -30 and -3 km s^-1, associated with the "expanding molecular ring at 300 pc" and with the spiral structure of our galaxy. The three lower velocity features have T_rot ⪉ 14 - 19K.